The present invention relates to a field effect transistor oscillator, operating at very high frequencies and having two yttrium garnet ball or pellet gyromagnetic resonators, electronically tunable in a very wide frequency range, while having within said range a good linearity of the frequency as a function of the magnetic control field of the resonators. The invention essentially relates to the coupling of the resonators to the gate and source of the field effect transistor.
Oscillators of the three-port type with field effect transistors and gyromagnetic resonators are known, but hitherto they have either had a wide frequency range or a good linearity. As a function of the configurations, the regulations or settings of the yttrium garnet resonator or resonators did not make it possible in known arrangements to improve the frequency range except if a less satisfactory linearity was accepted and vice versa.
The invention obviates this disadvantage by proposing a novel coupling between the resonators and the transistor resulting from the analysis of the operation of each resonator as a function of the frequency. According to the invention, each of them is coupled to the transistor so as to optimize the oscillation state towards the low frequencies for one resonator and towards the high frequencies for the other resonator. The term low and high frequencies is understood to mean, within the scope of the present invention, frequencies such as 4 and 22 GHz. Thus, the oscillator according to the invention has a wide frequency range between 4 and 22 GHz and also a good linearity within this range, whereas the known oscillators only have a range between 7 and 14 GHz for the same tolerance on the frequency linearity as a function of the control field.
The oscillator according to the invention has a field effect transistor, whose drain is loaded by an impedence, e.g. a standardized 50 ohm impedence, whose source is connected to a tuning dipole and whose gate is connected to a reaction dipole relooped on to the source across the tuning dipole. The tuning and reaction dipoles are constituted by iron-yttrium or gallium-yttrium-iron garnet balls or pellets. The first so-called gate ball, whose influence on the frequency preponderates at higher frequencies is coupled by a wire to the gate. The second ball, which is coupled to the source by a wire, has a preponderant influence at lower frequencies. In order to improve the linearity at low frequencies, permitting a greater swing towards the low frequencies, the second ball is doubly coupled, namely to the source by a wire and to the gate by the same wire which already couples the first ball.